1. Field of the Invention
The invention relates to a wall structure for an electric furnace.
2. Description of the Prior Art
Electric ovens, particularly those used for annealing, comprise large cavities or compartments having hangers disposed on the inside thereof and usually have a serpentine arrangement of electric resistance heater strips supported by the hangers. The walls of such furnaces are typically formed from an outer structural layer, oftentimes formed from sheet steel, and a heat insulating inner layer to which the hangers are secured. It has been the practice to form this inner layer from firebrick or other dense refractory materials. These dense refractory materials conduct substantial amounts of heat from the interior of the furnace to the outer shell thereby allowing the shell to heat to excessive temperatures. Allowing such heat to reach the outer shell lowers the overall efficiency of the furnace to unacceptable levels. The electric furnace wall construction of the present invention prevents excessive amounts of heat from being transferred from the interior of the furnace to the outer shell.
In normal use, the dense refractory materials or firebrick employed in prior art electric furnaces and the hangers used therein deteriorate requiring a periodic rebuilding of the walls. Due to the weight of the refractory materials employed in prior art electric furnace walls and the number of bricks required, this rebuilding is time-consuming and very costly, particularly with respect to the ceiling which usually must be domed. The rebuilding and any other routine maintenance of the electric furnace wall construction of the present invention may be performed economically in a minimal amount of time.
The firebrick and other refractory materials of prior art electric furnaces retain substantial quantities of heat. Thus, prior art electric furnaces require excessive amounts of time to reach operating temperature and to cool down therefrom which also lowers the overall efficiency of the furnace and therefore increases the costs of any manufacturing process in which heating in such a furnace is a required step. The electric furnace wall construction of the present invention does not retain such substantial amounts of heat and therefore lessens the amount of time required to heat to operating temperatures the interior of a furnace in which it is employed. Likewise, the time period required for cooling an electric furnace employing the wall construction of the present invention is also lessened. Therefore, an electric furnace employing the wall construction of the present invention is more efficient to operate than prior art electric furnaces and therefore makes manufacturing processes in which such a furnace is employed less costly.
Finally, the high densities of the firebrick and refractory materials employed in prior art furnaces make the furnace doors extremely heavy and therefore cumbersome to operate. However, the electric furnace wall construction of the present invention is light in weight compared to such prior art furnace walls making the doors employing the construction of the present invention relatively light in weight and easy to operate.
Therefore, it is an object of the present invention to provide an electric furnace wall construction having heat insulative properties which present an outer shell of an electric furnace which employs such a construction from reaching excessive temperatures when the furnace is operating.
It is another object of the present invention to provide an improved electric furnace wall construction which is capable of being rebuilt and routinely maintained at relatively low costs and in minimal amounts of time.
It is another object of the present invention to provide an improved electric furnace wall construction which retains relatively small quantities of heat.
It is another object of the present invention to provide an improved electric furnace wall construction which is relatively light in weight making a door in which the construction is employed easy to operate.